Switching amplifier having linear transition totem pole modulation

Abstract

A switching amplifier includes a first portion of a power stage; a second portion of a power stage; a pulse-width modulation (PWM) control loop coupled to control inputs of the first portion of the power stage; and a linear amplifier coupled to control inputs of the second portion of the power stage. The PWM control loop controls a first switch and a second switch of the first portion of the power stage. Between current terminals of the first switch and the second switch is a first signal output of the switching amplifier. The linear amplifier controls a third switch and a fourth switch of the second portion of the power stage. Between current terminals of the third switch and the fourth switch is a second signal output of the switching amplifier.

What is claimed is:  
     
       1. An apparatus, comprising:
 a control circuit having an input, first control outputs, and second control outputs, the control circuit including a filter and a modulation signal generator coupled between the input and the first control outputs and an amplifier coupled between the input and the second control outputs; 
 a first power stage having first control inputs and a first power stage output, the first control inputs coupled to the first control outputs; 
 a second power stage having second control inputs and a second power stage output, the second control inputs coupled to the second control outputs. 
 
     
     
       2. The apparatus of  claim 1 , wherein the input is a first input, and the control circuit has a second input; and
 wherein the filter is a loop filter having a first filter input, a second filter input and a filter output, the first filter input coupled to the first input and the first power stage output, and the second filter input coupled to the second input and the second power stage output. 
 
     
     
       3. The apparatus of  claim 1 , wherein the amplifier is a linear amplifier. 
     
     
       4. The apparatus of  claim 1 , wherein the first power stage has a first power supply terminal, and the second power stage has a second power supply terminal; and
 wherein the amplifier is configured to generate control signals to clamp the second power stage output at a voltage of the second power supply terminal. 
 
     
     
       5. The apparatus of  claim 4 , wherein the first power stage includes:
 a first transistor coupled between the first power supply terminal and the first power stage output, the first transistor having a first control terminal coupled to a first one of the first control inputs; and 
 a second transistor coupled between the first power stage output and a ground terminal, the second transistor having a second control terminal coupled to a second one of the second control inputs; and 
 wherein the second power stage includes:
 a third transistor coupled between the second power supply terminal and the second power stage output, the third transistor having a third control terminal coupled to a first one of the second control inputs; and 
 a fourth transistor coupled between the second power stage output and the ground terminal, the fourth transistor having a fourth control terminal coupled to a second one of the second control inputs. 
 
 
     
     
       6. The apparatus of  claim 1 , wherein the first power stage output is coupled to an inductor terminal, and the second power stage output is coupled to a capacitor terminal. 
     
     
       7. The apparatus of  claim 1 , wherein the control circuit, the first power stage, and the second power stage are part of an integrated circuit. 
     
     
       8. The apparatus of  claim 1 , wherein the control circuit, the first power stage, and the second power stage are part of an audio amplifier. 
     
     
       9. The apparatus of  claim 2 , further comprising:
 a first resistor coupled between the first input and the first filter input; 
 a second resistor coupled between the second input and the second filter input; 
 a third resistor coupled between the first filter input and the first power stage output; and 
 a fourth resistor coupled between the second filter input and the second power stage output. 
 
     
     
       10. The apparatus of  claim 2 , wherein the modulation signal generator is a pulse width modulation signal generator and includes: a summer having a first summer input, a second summer input, and a summer output, the first summer input coupled to the filter output, the second summer input coupled to the second power stage output; and a comparator having a first comparator input, a second comparator input and a comparator output, the first comparator input coupled to the summer output, the second comparator input coupled to a ramp reference terminal, and the comparator output coupled to the first control outputs. 
     
     
       11. A system, comprising:
 a control circuit having an input, first control outputs, and second control outputs, the control circuit including a filter and a modulation signal generator coupled between the input and the first control outputs and an amplifier coupled between the input and the second control outputs; 
 a first power stage having first control inputs and a first power stage output, the first control inputs coupled to the first control outputs; 
 a second power stage having second control inputs and a second power stage output, the second control inputs coupled to the second control outputs; 
 an inductor coupled between the first power stage output and a first output; and 
 a capacitor coupled between the first output and the second power stage output. 
 
     
     
       12. The system of  claim 11 , wherein the input is a first input, the control circuit has a second input; and
 wherein the filter is a loop filter having a first filter input, a second filter input and a filter output, the first filter input coupled to the first input and the first power stage output, and the second filter input coupled to the second input and the second power stage output. 
 
     
     
       13. The system of  claim 12 , wherein the amplifier is a linear amplifier. 
     
     
       14. The system of  claim 11 , wherein the first power stage has a first power supply terminal, and the second power stage has a second power supply terminal; and
 wherein the amplifier is configured to generate control signals to clamp the second power stage output at a voltage of the second power supply terminal. 
 
     
     
       15. The system of  claim 14 , wherein the first power stage includes a first transistor coupled between the first power supply terminal and the first power stage output, the first transistor having a first control terminal coupled to a first one of the first control inputs, and a second transistor coupled between the first power stage output and a ground terminal, the second transistor having a second control terminal coupled to a second one of the second control inputs; and
 wherein the second power stage include a third transistor coupled between the second power supply terminal and the second power stage output, the third transistor having a third control terminal coupled to a first one of the second control inputs, and a fourth transistor coupled between the second power stage output and the ground terminal, the fourth transistor having a fourth control terminal coupled to a second one of the second control inputs. 
 
     
     
       16. The system of  claim 11 , wherein the capacitor is a first capacitor, and the system further comprises a second capacitor coupled between the second power stage output and a ground terminal. 
     
     
       17. The system of  claim 11 , further comprising a speaker coupled between the first output and the second power stage output. 
     
     
       18. The system of  claim 11 , wherein the control circuit, the first power stage, and the second power stage are part of an integrated circuit. 
     
     
       19. The system of  claim 11 , wherein the control circuit, the first power stage, and the second power stage are part of an audio amplifier. 
     
     
       20. The system of  claim 12 , further comprising:
 a first resistor coupled between the first input and the first filter input; 
 a second resistor coupled between the second input and the second filter input; 
 a third resistor coupled between the first filter input and the first power stage output; and 
 a fourth resistor coupled between the second filter input and the second power stage output. 
 
     
     
       21. The system of  claim 12 , wherein the modulation signal modulator is a pulse with modulation (PWM) signal generator and includes: a summer having a first summer input, a second summer input, and a summer output, the first summer input coupled to the filter output, the second summer input coupled to the second power stage output; and a comparator having a first comparator input, a second comparator input and a comparator output, the first comparator input coupled to the summer output, the second comparator input coupled to a ramp reference terminal, and the comparator output coupled to the first control outputs. 
     
     
       22. A method comprising:
 receiving a first signal; 
 filtering the first signal using a filter; 
 generating first control signals from the filtered first signal using a modulation signal generator; 
 generating second control signals from the first signal using an amplifier; 
 generating a second signal by providing the first control signals to a first power stage; and 
 generating a third signal by providing the second control signals to a second power stage. 
 
     
     
       23. The method of  claim 22 ,
 wherein generating the first control signals includes generating the first control signals using the second signal as a feedback signal. 
 
     
     
       24. The method of  claim 22 , wherein generating the first control signals includes:
 generating a summation signal based on a sum between the filtered first signal and the third signal; 
 comparing the summation signal with a ramp signal to generate a comparison signal; and 
 generating the first control signals as pulse width modulation signals based on the comparison signals. 
 
     
     
       25. The method of  claim 22 ,
 wherein the amplifier is a linear amplifier. 
 
     
     
       26. The method of  claim 22 , further comprising clamping the third signal at a supply voltage.